Field of the Invention
The present invention relates to an electrode structure of a semiconductor device and a method of manufacturing the same.
Description of the Background Art
A package such as a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor) which is a power semiconductor device is often formed by resin sealing through transfer molding in respect of a manufacturing cost, a productivity and the like.
Japanese Patent No. 5012772 discloses that an electrode erected on a surface of a sealing resin is exposed in consideration of reduction in size of the device and convenience of wiring. Moreover, Japanese Patent Application Laid-Open No. 2012-74543 discloses the technique for reducing a power loss by using a direct lead bonding method for directly connecting an emitter electrode and a lead terminal in place of connection of both the electrodes through a bonding wire in a semiconductor device subjected to transfer molding. Moreover, it is described that an electrode post erected and bonded onto a plate electrode is exposed to an outside.
In a semiconductor device using an SiC chip, particularly, there is some action for development to aim at an operation at 175° C. or more which is higher than an IGBT according to the related art. When a request for the high temperature operation is given to the semiconductor device described in the Japanese Patent Application Laid-Open No. 2012-74543, it is desirable that the external electrode should be bonded through ultrasonic bonding in place of solder bonding.
In the case where an ultrasonic bonding method is used, however, there is a fear that a bonding portion on a base of an electrode post exposed to the outside might be molten due to transmission of heat generated in the bonding to the bonding portion. Furthermore, there is also a fear that breakdown such as a crack might occur in the bonding portion due to an ultrasonic vibration. In particular, an electrode on an emitter side (a source side) disposed on a direct lead diffuses heat in the bonding with more difficulty than an electrode on a collector side (a drain side) to be bonded to a structure for dissipating heat, for example, a heat spreader, so that a possibility of breakdown is higher.